1. Field of the Invention
This invention relates to the drilling of boreholes in the earth. It relates especially to methods and downhole assemblies, one downhole assembly being used to increase the angle of deviation of the wellbore from the vertical, and the other bottom hole assembly being used for decreasing the angle of deviation of the borehole from the vertical. It also relates especially to special equipment used in the bottom hole assembly to effect the desired drilling.
2. Setting of the Invention
Oil and gas are produced from underground formations through wellbores drilled from the surface to the formation. Originally, it was desired to drill the well in as nearly a vertical direction as possible. However, in some cases, due to the particular geometry of the underground formation, it is nearly impossible to drill vertical wells. This is particularly true in steeply dipping formations in which the well keeps wanting to veer off to the updip side. Means are then required to cause the well to drill in the opposite direction. These tools which have been used for this purpose are ordinarily called directional drilling tools. Recently, it has become increasingly popular to drill wells in oriented directions. This is particularly true of offshore production. In those areas, a platform may be erected in water 100 to 200 feet or more deep, and many wells drilled from a single platform. The wells will not be drilled in a vertical position, but will be drilled in a slanting or directional position in order to reach a particular subsurface location in the producing formation, which may be 1 or 2 miles in a lateral direction from the location of the platform.
There are numerous directional drilling tools, and there have also been numerous articles published on directional drilling techniques. One of the earliest and still one of the best articles published on the use of stabilizers in downhole assemblies used in controlling hole deviation is the article by H. B. Woods and Arthur Lubinski, entitled "Use of Stabilizers in Controlling Hole Deviation," and presented at the Spring Meeting of the Mid-Continent District Division of Production, Amarillo, Tex., March 1955, and published in Drilling and Production Practice, 1955. As stated in that article, when weight is applied to their bottom hole assembly, there is a force which is detrimental when weight is applied, because it tends to direct the hole away from vertical. We teach a method whereby the bottom hole assembly can be selected and in which weight can be applied and still decrease the angle of deviation; or, if desired, we can select a bottom hole assembly to increase the direction of deviation.